There are a number of reasonably well documented equations and soil moisture model (or "Topographic Wetness Index, TWI) approaches for calculating soil moisture parameters using a raster digital elevation model. The calculations (which I'm guessing have evolved over the past few years) are simply a function of the slope and the contributing upslope area; with the basic understanding that, all things (such as land cover and soil catenas) being equal, the bottom of a long slope slope will tend to be wetter than the top of a short slope. Some of the older hydrological software addons to ArcGIS (TauDEM, etc...) even have Soil Moisture functions included. The simplistic notation is: LN (a/S) or the natural log of the Upslope Area divided by the slope (for all points\pixels within the DEM).
H. Mitasova has been working on the geospatial estimation of such estimates (which can easily be built into scripted functions within packages such as ArcGIS with Spatial Analyst (as well as Open Source software such as GRASS)... For more see: http://naldc.nal.usda.gov/download/44278/PDF http://skagit.meas.ncsu.edu/~helena/gmslab/reports/CerlErosionTutorial/denix/Advanced/ErosionRep97/rep97.html http://hydrology.usu.edu/RRP/userdata/4/87/Appendices.pdf http://ks.water.usgs.gov/pubs/reports/wrir.99-4242.html http://journalofmaps.com/student/10_01_Hardy.pdf John Mickelson Geospatial and Ecological Services 501 Stage Rd. Monroe, NY 10950-3217 (845) 893-4110 [email protected] ________________________________ From: Alexandre Fadigas de Souza <[email protected]> To: [email protected] Sent: Wednesday, August 28, 2013 10:00 PM Subject: [ECOLOG-L] Soil humidity from topographic data? Dear friends, I have a number of soil-related variables, and need to estimate soil humidity. Would someone know how? We have collected topographic (elevation, slope, convexity), soil (texture and nutrients), and vegetation cover data from 85 5 x 5 m plots scattered through a sandy coastal vegetation complex in northeastern Brazil, which include sand dunes as well as latosols. We did not have enough funding or time to measure soil humidity in the filed, but our analyses would greatly benefit from an estimation of it. Do you have an idea on how to do that? Many thanks, Alexandre
